Paramedian Lobule Research Articles

Trigeminocerebellar projections to the posterior lobe in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

Cerebellar projections of the nucleus interpolaris and oralis of the spinal trigeminal nucleus were studied in the cat by anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Injections of WGA-HRP into these nuclei labeled many mossy fiber terminals mainly ipsilaterally in the rostral folium of lobule IX (IXa or IXa + b), the simple lobule, the anterior part (sublobule A) of the paramedian lobule and the posterior part of crus II. Labeled terminals were also seen in the anterior lobe, lobules VI and VII, the anterior part of crus I, and the paraflocculus dorsalis. Projection fields in the horizontal plane of lobules were reconstructed from a series of transverse sections through each folium of lobule IX, the paramedian lobule, and the posterior part of crus II on the ipsilateral side. In sublobule IXa + b, labeled terminals were distributed in five longitudinal areas extending along the apicobasal axis of the sublobule. These five areas were located in the apical two-thirds of the ipsilateral half of the sublobule. Labeled terminals were distributed in five longitudinal areas in sublobule A (the rostral part) of the paramedian lobule. In the posterior part of crus II, four aggregations of labeled terminals were present in cross sections through a lobule. They were distributed in the apicobasal extent of the lobules. The present study indicates that the projection fields of trigeminocerebellar fibers are longitudinally arranged along the apicobasal axis of the cerebellar lobules.

Development of the paramedian lobule of the cerebellum in wild-type and tottering mice.

The mutant mouse tottering, (tg/tg), and the compound heterozygote mouse (tg/tg1a) exhibit three neurological disorders: ataxia, petit mal-like absence seizures and myoclonic intermittent movement disorders which are independent of the absence seizures. The tottering mouse carries an autosomal recessive single gene mutation on chromosome 8, and behavioral symptoms are first observed in the 3rd to 4th week of age. Using an additional genetic marker, Oligosyndactyly (Os), it is possible to distinguish tg/tg and tg/tg1a mice from wild-type mice at birth; nonaffected heterozygous littermates carry the Os mutation while tottering and compound heterozygous mice do not carry the Os gene. Similar to neurons found elsewhere in the brain, cerebellar Purkinje cells in both the wild-type and mutant mice were found to decrease in diameter with maturation. Forebrain weight, hindbrain weight, Purkinje cell dimensions and the thickness of the molecular layer in the paramedian lobule of the cerebellum in mutant mice were found to be reduced in mutants after, but not prior to the onset of behavioral symptoms.

Exercise and the brain: angiogenesis in the adult rat cerebellum after vigorous physical activity and motor skill learning.

This study compared the morphology of cerebellar cortex in adult female rats exposed for 1 month to repetitive exercise, motor learning, or an inactive condition. In the exercise conditions, rats that were run on a treadmill or housed with access to a running wheel had a shorter diffusion distance from blood vessels in the molecular layer of the paramedian lobule when compared to rats housed individually or rats that participated in a motor skill learning task. Rats taught complex motor skills substantially increased the volume of the molecular layer per Purkinje neuron and increased blood vessel number sufficiently to maintain the diffusion distance. These results dissociate angiogenesis associated with increased neuropil volume (as seen in the motor learning group) from angiogenesis associated with increased metabolic demands (as seen in the exercise groups). While the volume fraction of mitochondria did not differ among groups, the mitochondrial volume fraction per Purkinje cell was significantly increased in the motor skill rats. This appears to parallel the previously reported increase in synapses and associated neuropil volume change.

Non-reciprocal connections between the vestibular nuclei and the cerebellar paramedian lobule, with special reference to the climbing fiber zones: an analysis in the rabbit using the retrograde horseradish peroxidase method

The organization of the secondary vestibular projections onto the cerebellar paramedian lobule (PML) and possible reciprocal corticovestibular connections were investigated by the retrograde horseradish (HRP) technique in the rabbit. Following injections of the tracer into the vestibular nuclear complex (VNC), an ill-defined, sagittal band composed of numerous labelled Purkinje cells was found ipsilaterally throughout the length of the lateral portion of the vermis, the ventral paraflocculus and the flocculus. However, no labelled Purkinje cells were found in the cortex of the PML. The results indicate that zone B, considered to give rise to cerebellar corticovestibular projections, is not present in the rabbit PML. After injections of HRP into the PML, the retrograde labelling pattern in the VNC was analyzed, in relation to the climbing fiber zones identified by retrograde labelling in the inferior olive. No clear-cut correspondence could be found between the vestibular subdivisions and climbing fiber zones in the PML, except that only the interstitial nucleus of the vestibular nerve projects into zone D 1 in sublobules e and d. There were no vestibular projections to zone D 2. The only salient feature was that cells projecting onto zones C 2, C 1 and C 3 of the PML were arranged rostrocaudally in the inferior vestibular nucleus and the caudal portion of the medial vestibular nucleus. In addition, a topical relationship was found between parts of the VNC and sublobules of the PML.

Toxic effects of somatostatin in the cerebellum and vestibular nuclei: multiple sites of action

This study demonstrates that somatostatin (SRIF), an endogenous peptide in vestibular nuclei and cerebellum, can produce both a dose-dependent death of Purkinje cells in distinct sagittal regions of cerebellar cortex and vascular infarcts centered selectively in the inferior vestibular nucleus. Alert, adult male rats were given a 5 μl intracerebroventricular (i.c.v.) bolus of either SRIF alone (20 or 40 μg) or a combined dose of SRIF plus either arginine-vasopressin (AVP, 1 μg) or an AVP V1 antagonist, (1-(β-mercapto-β,β-cyclo-pentamethylene propionic acid), 2-( O-methyl)-tyrosine)-arginine 8-vasopressin (mcAVP, 1 μg), through an implanted cannula. After a 4–5 day survival, the brains were stained with the cupric-silver selective degeneration method. Two types of dose-dependent lesions were observed in the cerebellar and vestibular nuclei of these animals: degeneration of Purkinje cell responses in the cerebellar cortex and vascular infarcts in vestibular nuclei. These toxic responses were unaffected by application of AVP or mcAVP; hence, they can be attributed to actions of SRIF. The distribution of Purkinje cell degeneration varied with the SRIF dose in different cerebellar regions. Purkinje cell responses in lobules I–III were equivalent at both SRIF doses, and degeneration in the copula pyramis, paraflocculus and paramedian lobule emerged at the higher SRIF dose. Purkinje cells in the medial aspect of lobules IX–X had an intermediate sensitivity to SRIF intoxication. Degenerating Purkinje cells tended to be arranged in parasagittal bands in each region, suggesting parasagittal zonal variations in susceptibility to SRIF intoxication. By contrast, infarctions in the vestibular nuclei only appeared at the higher SRIF dose. These infarcts could be unilateral or bilateral and always involved the inferior vestibular nucleus at the level of the caudal margin of the acoustic tubercle; they often extended into the medial and lateral vestibular nuclei. The infarcts had a necrotic core that was infiltrated by non-neuronal elements. Thus, they appear to reflect a direct or neurally-mediated vascular response to the peptide.

Stimulus classification by ensembles of climbing fiber receptive fields

Although the local structure of the cerebellum is fairly uniform and its inputs are often widely shared, outputs from different regions of the cerebellar cortex reach different parts of the cerebellar and vestibular nuclei, which can affect the rest of the nervous system in different ways. In this review, we explain how different ensembles of climbing fiber responses in the anterior lobe and paramedian lobule can be generated by a tactile stimulus to the distal hindpaw. Apart from differing in degree of activation, the cortical regions differ also in the detailed pattern of the activation transmitted. The anterior lobe can distinguish a greater diversity of stimuli to various skin surfaces than can the paramedian lobule. This differential classification of particular stimulus arrays by the two cerebellar regions could produce distinct patterns of neuronal activity in various corticonuclear compartments.

Topographical organization in the origin of serotoninergic projections to different regions of the cat cerebellar cortex

The distribution of serotonin immunoreactivity in the cat cerebellum was studied by using the indirect antibody peroxidase-antiperoxidase (PAP) technique. Furthermore, the origin of these chemically defined afferents was determined by combining the retrograde transport of horseradish peroxidase (HRP) with the PAP technique. In the cerebellar cortex, serotonin immunoreactivity is present in a plexus of beaded fibers that is confined almost exclusively to the granule and Purkinje cell layers; a few fibers are present in the molecular layer. Serotoninergic axons and varicosities have a dense and uniform distribution throughout all lobules of the cerebellum with the exception of lobule X where the fiber density is sparse. Serotonin cell bodies were not found within the cerebellar cortex. However, following pretreatment with pargyline and L-tryptophan, serotonin positive cell bodies were found in all deep cerebellar nuclei as well as the raphe and reticular nuclei in the brainstem. The present study demonstrates that the serotoninergic projection to the cat's cerebellum has some degree of topographical organization. Serotoninergic fibers in the anterior vermis (lobules I-V) were shown to arise from neurons located within the paramedian reticular nucleus, the lateral reticular nucleus, and the lateral tegmental field. Injections of HRP into either the posterior vermis (lobule VI-IX) or the paramedian lobule, labeled serotoninergic neurons exclusively in the lateral reticular nucleus. Lobus simplex, crus I and crus II (the hemisphere) receive a serotoninergic input from cells located in the lateral tegmental field, the peri-olivary reticular formation and the paramedian reticular nucleus. In no cases were neurons in the raphe double-labeled, although there were cells positive for HRP or serotonin alone. The data indicate that there is a topographical organization in the serotoninergic projection from the caudal brainstem to specific regions of the cat's cerebellar cortex. In addition to climbing and mossy fibers, this projection represents a third major source of cerebellar afferents based on its dense and widespread distribution as well as its morphological and chemical characteristics.

Choline acetyltransferase immunoreactivity in the cat cerebellum

Choline acetyltransferase immunoreactivity was demonstrated in particular projection systems in cat cerebellum by combining immunohistochemistry, retrograde tracing and lesioning paradigms. The monoclonal antibody used in this study recognized a 68,000 mol. wt protein on immunoblots of cat cerebellum and striatum. Choline acetyltransferase immunoreactivity was localized to some neurons and varicose fibers in the cerebellar nuclei, and also to some mossy fibers and endings (rosettes), fiber plexuses around Purkinje cells, granule cells and parallel fibers in the cerebellar cortex. In addition, the presence of choline acetyltransferase-immunoreactive large cells, presumptive Golgi cells, in the granular layer was confirmed. In each cerebellar nucleus, choline acetyltransferase-immunoreactive neurons contained either large, medium-sized or small cell bodies and were distributed evenly in the entire nuclear domain. Large and medium-sized ones were frequently encountered. Choline acetyltransferase-immunoreactive mossy fibers and rosettes were most abundant in the vermal lobules I–III, VIII, IX and the simple lobule, moderately accumulated in the vermal lobules IV–VII, X, crus I and crus II, and less abundant in the paramedian lobule, paraflocculus and flocculus. Some granule cells with prominent dendritic claws and bifurcating parallel axons were immunolabeled in the entire vermis with infrequent occurrence in the remaining cortices. Following unilateral lesioning of the cerebellar nuclei with electrocoagulation or kainate injections, a reduction in number of choline acetyltransferase-immunoreactive fibers occurred ipsilaterally in the cerebellar cortex and contralaterally in the red nucleus, ventrolateral thalamic nucleus and ventroanterior thalamic nucleus. In addition, perikarya of some cerebellothalamic neurons were shown to contain choline acetyltransferase immunoreactivity. The results indicate that some nucleocortical, cerebellorubral and cerebellothalamic projections are cholinergic and that a subpopulation of cholinergic granule cell-parallel fibers exists.

Neuronal activity in the lateral cerebellum of trained monkeys, related to visual stimuli or to eye movements.

1. The responses of neurones in the lateral cerebellar cortex to visual stimuli and to eye movements were recorded in rhesus monkeys trained to perform visually guided arm and eye movements in a tracking task. 2. Twenty-two of 134 units recorded (16%) modulated their discharge in response to a bright Xenon flash. They were mainly located in the dorsal paraflocculus. Among those identified as Purkinje cells both simple spike and climbing fibre responses to the flash were seen. (72% of the units were related to arm movements; these were centred in the paramedian lobule, and have been described fully in Marple-Horvat & Stein (1987).) 3. The visual responsiveness of one of the units varied according to the phase of the monkey's task. Around the time that the target stepped, which was the monkey's cue to move, its sensitivity to other stimuli disappeared. 4. Only two neurones responded to the movements of the tracking target. These responses were conditional upon the monkey using visual signals to guide his movements; they did not respond to the target step if he moved before the target did. 5. Fourteen units (10%) located in crus I and II and lobulus simplex correlated strongly with the velocity of horizontal eye movements. Only one of these also responded to visual stimuli. 6. Thus most neurones were found to carry only visual, or eye movement, or limb movement information rather than combinations of these signals; they were located in different but overlapping regions of lateral cerebellar cortex. Visually responsive neurones are probably involved in planning the visual goal of movements, while eye and arm movement neurones probably help to create co-ordinative structures for executing voluntary eye and arm movements.

Learning causes synaptogenesis, whereas motor activity causes angiogenesis, in cerebellar cortex of adult rats.

The role of the cerebellar cortex in motor learning was investigated by comparing the paramedian lobule of adult rats given difficult acrobatic training to that of rats that had been given extensive physical exercise or had been inactive. The paramedian lobule is activated during limb movements used in both acrobatic training and physical exercise. Acrobatic animals had greater numbers of synapses per Purkinje cell than animals from the exercise or inactive groups. No significant difference in synapse number or size between the exercised and inactive groups was found. This indicates that motor learning required of the acrobatic animals, and not repetitive use of synapses during physical exercise, generates new synapses in cerebellar cortex. In contrast, exercise animals had a greater density of blood vessels in the molecular layer than did either the acrobatic or inactive animals, suggesting that increased synaptic activity elicited compensatory angiogenesis.

Locomotion‐related variations in excitability of spino‐olivocerebellar paths to cat cerebellar cortical c2 zone.

1. Cutaneous nerve stimulation was used to study the excitability of the spino-olivocerebellar pathways (SOCPs) to the c2 zone of the paravermal cerebellar cortex in the cat. Non-noxious single-shock stimulation of the right and left superficial radial (SR) nerves via implanted cuff electrodes was used to evoke field potentials in the cerebellar cortex via the SOCPs. 2. The evoked potentials were recorded extracellularly either in lobule V of the anterior lobe (three cats) or within the paramedian lobule of the posterior lobe (one cat) with glass-coated tungsten microelectrodes. Measurement of the amplitudes of the responses was used to monitor transmission in the SOCPs in cats at rest and during walking. 3. A total of eleven c2 recording sites were investigated in detail. At seven of these sites, responses were recorded both during locomotion and at rest. For all seven sites responses during locomotion were smaller, more variable in amplitude and less securely evoked (average reduction 59%). 4. At five out of the eleven recording sites (45%) the mean amplitude of responses elicited during different tenths of the step cycle fluctuated sufficiently that the largest response was more than twice the smallest. In the majority of these cases (4/5) the responses were largest in either mid-stance or late swing. These fluctuations in response size occurred without parallel fluctuation in the amplitude of the peripheral nerve volley. At the remaining sites fluctuation of the cerebellar field size was less and in some cases practically absent. 5. At six recording sites it was possible to record the climbing fibre potentials evoked by stimulation of both the ipsilateral and contralateral superficial radial nerves. In all six cases the fluctuations in size of the response during locomotion occurred in phase, despite the fact that the two limbs move out of phase. 6. The probability that an individual stimulus would evoke any cerebellar response also varied between the different tenths of the step cycle and such variations occurred in parallel with the fluctuations in response size. This shows that the SOCP regulatory mechanism(s) must, at least in part, operate at a precerebellar level.

The projection of spinocerebellar neurons from the sacrococcygeal region of the spinal cord in the cat. An experimental study using anterograde transport of WGA-HRP and degeneration.

The projection from the sacro-coccygeal region of the spinal cord to the cerebellum was studied by two different techniques in the cat. In five cats wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) was injected caudal to a preceding unilateral cordotomy at the sacral level, aimed at interrupting the spinocerebellar tracts on one side completely, and the distribution of WGA-HRP labeled mossy fibers and mossy fiber terminals was studied in the cerebellum. In three additional cats, degenerating fibers were examined in Fink-Heimer stained sections following unilateral transection of the lateral and ventral funiculi at L7 or S3 level. In the WGA-HRP experiments the labeled mossy fiber terminals were located bilaterally in lobules I-V. Most of them were found in the anterior part of lobule II. In addition, labeled terminals were observed in sublobule VIIIB and in pars copularis of the paramedian lobule, contralateral to the cordotomy. The terminals in the anterior lobe were concentrated in longitudinal zones parallel to the mid sagittal plane. In lobule II, the terminals were most abundant in the superficial, apical parts of the folia. Some presumed terminals were also seen in the cerebellar nuclei. Labeled fibers were found contralateral, but not ipsilateral to the cordotomy in the superior and inferior cerebellar peduncles, as well as in the spinal cord rostral to the cordotomy. The results of the degeneration experiments were the same as those of the WGA-HRP experiments with regard to the detailed projections in the cerebellar cortex. This is strong support against the possibility that WGA-HRP labeled cerebellar mossy fiber terminals, following WGA-HRP injections in the spinal cord, would represent terminals of collaterals of retrogradely labeled neurons. It also lends strong support in favour of WGA-HRP as a reliable anterograde tracer for studying cerebellar cortical projections of spinocerebellar neurons in the cat.

Topographical localisation in the projections from the inferior olive to the paravermal cortex of the anterior lobe and paramedian lobule in the cerebellum of the cat. A brief review.

Topographical localisation in the projections from the inferior olive to the paravermal cortex of the anterior lobe and paramedian lobule in the cerebellum of the cat. A brief review.

The lateral reticular nucleus in the cat

Intracellular recording from neurones in the lateral reticular nucleus (LRN) demonstrated that, in addition to the previously identified excitatory ipsilateral forelimb tract (iF tract) (Clendenin et al. 1974c) there is an inhibitory tract mediating information from the ipsilateral forelimb to the LRN. The excitatory and inhibitory tracts were similarly organized. The tract neurones were monosynaptically activated by afferents in the ipsilateral forelimb and projected to the same area of the LRN. They will be considered as excitatory and inhibitory components of the iF tract and denoted the excitatory and inhibitory iF tract (EiF and IiF tracts). Stimulation of the descending ipsilateral dorsolateral funiculus (iDLF) in the C3 segment evoked disynaptic EPSPs and IPSPs in LRN neurones contacted by the EiF and IiF tracts. The responses in individual LRN neurones evoked from the iDLF were similar to the responses evoked from the forelimb nerves suggesting that the EiF and IiF tracts are monosynaptically activated by fibres in the iDLF. The dorsal portion of the magnocellular part of the LRN constituted the main termination area of both the EiF and IiF tracts. Neurones in this area have previously been shown to project ipsilaterally to lobule V in the pars intermedia of the cerebellar anterior lobe and to the paramedian lobule (Clendenin et al. 1974a). IPSPs evoked from the IiF tract in LRN neurones outside the main termination area had smaller amplitudes and longer latencies. This finding suggests that these responses were generated by thin axon collaterals given off from dorsally located stem axons.

Topographic and zonal pattern of olivocerebellar projection to the paramedian lobule in the rabbit: an experimental study with an HRP retrograde tracing method

Distribution of neurons in the inferior olive (IO) projecting to the paramedian lobule (PML) was studied in rabbits by means of retrograde transport of horseradish peroxidase (HRP). HRP was injected into various regions of different folia of the PML. Findings indicate zonal and to some extent topographic organization in olivocerebellar projections to PML folia. The neurons in corresponding areas of dorsal (dlPO) and ventral lamina (vlPO) of the principal olive (PO) project to composite zones D (D 1 + D 2) in sublobule f: medial, intermediate and lateral. In addition, the caudal part of the medial accessory olive (MAO) projects to the most laterally located zone (C 2-lateral) and the caudal part of the dorsal accessory olive (DAO) to the most lateral zone (C 3) in sublobule f. The middle part of the DAO sends projections to zone C 1 located medially in sublobules d-a. The rostral and caudal parts of the DAO send projections to zone C 3 in sublobules a and f, respectively. The rostral, middle and adjacent caudal parts of MAO, with no clear topographic organization, project to broad zone C 2 in sublobules e-b. The neurons in restricted areas of the caudomedial part of the dlPO and vlPO, probably intermingled with those supplying the composite medial zone D in sublobule f, project to sublobules e-b to terminate in zones D 1 and D 2, respectively.

Spinocerebellar projections from spinal border cells in the cat as studied by anterograde transport of wheat germ agglutinin‐horseradish peroxidase

The cerebellar projections of spinal border cells, which give rise to crossed ascending axons, were studied in the lower lumbar segments by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. Prior to the injections, the spinal cord was lesioned rostral and ipsilateral to the WGA-HRP injections to eliminate labeling of the ipsilaterally ascending axons. Following injections of WGA-HRP into the L4-L6 segments, labeled terminals were seen in sublobules Ib-Vf of the anterior lobe, sublobules VIf-VIe, lobule VIII, the paramedian lobule, and crus II. More than 90% of the total number of labeled terminals were in the anterior lobe; the projections were predominantly ipsilateral to their cells of origin (about 90% or more labeled terminals of the total number in each of sublobules IIb-Va). Many labeled terminals were seen ipsilaterally in sublobules IIb (11.1-17.5% of the total number), IIIa (11.7-12.9%), IIIb (16.1-17.6%), IVa (8.8-10.8%), IVb (6.2-10.5%), and Va (9.7-10.3%). In the posterior lobe, labeled terminals were numerous only in sublobule C of the ipsilateral paramedian lobule (2.7-4.9%). The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross-sections through each lobule. In the anterior lobe, labeled terminals were distributed in four major areas. In sublobules IIa-IVa, area 1 was located between 1.0 and 2.0 mm lateral to the midline in zones B-C1 of Voogd; area 2, between 2.0 and 3.0 mm lateral to the midline in zones C1-C2; area 3, between 3.0 and 4.0 mm in zones C2-C3; and area 4, lateral to 4.0 mm from the midline in zone C3. These areas extended apicobasally in the apical to middle parts of the lobules. On the rostral side of sublobule C1 of the ipsilateral paramedian lobule, the projection areas extended in the entire apicobasal and the mediolateral axis of the sublobule, except in the most lateral part. The present results suggest that the SBCs project to specific areas in the cerebellar lobules.

Simple spike discharge patterns of Purkinje cells in the paramedian lobule of the cerebellum during locomotion in the awake cat

Purkinje cells in the paravermal cortex of the paramedian lobule in the cerebellum of awake cats have been recorded during locomotion on a moving belt. The discharges of all 35 recorded cells exhibited frequency modulation that was time-locked to the step cycle. Most cells showed increased activity during late flexion or at the onset of the stance phase of the step in the ipsilateral forelimb. This observation is consistent with the hypothesis that the role played by the paravermal cortex during locomotion is in the coordination and timing of the transition between the stance and swing phases of the step.

Axonal branching of the olivocerebellar projection in the rat: A double‐labeling study

Collateralization of olivocerebellar (climbing) fibers was studied in the rat by means of the fluorochrome double-labeling technique. Most of the olivocerebellar projection is crossed except for a minimal ipsilateral component which arises from the most rostal part of the inferior olivary nucleus (ION). ION neurons in the caudolateral part of the medial accessory olive (MAO) and the dorsal accessory olive (DAO) give off axons that branch to supply both hindlimb areas of the contralateral cerebellar cortex, i.e., the rostral anterior lobe and the caudal paramedian lobule. In addition, neurons in the middle one-third of the contralateral MAO and DAO send axons that divide to terminate in both the caudal part of the anterior lobe and the rostral part of the paramedian lobule (forelimb receiving areas). Neurons within the caudal part of the MAO, the lateral part of the DAO, the ventral lamella of the principal olive (PO), and the dorsomedial cell column (DMCC) send axonal branches that terminate within at least two different areas of the same sagittal zones throughout the contralateral cerebellar cortex. Thus, the ION contains specialized cells that provide a divergence of integrated information from the ION to at least two cerebellar regions.

Spinocerebellar projections from the upper lumbar segments in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The projection fields of the dorsal spinocerebellar tract (DSCT) arising from Clarke's column, marginal neurons of Clarke's column, and lamina V neurons in the upper lumbar segments were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. To label only these neuron groups with uncrossed ascending axons, the spinal cord was lesioned rostral and contralateral to the WGA-HRP injections. Following injections of WGA-HRP into the L1-L4 segments, labeled terminals were seen in sublobules Ia-VIc and VIIb-VIIIb, the simple lobule, the paramedian lobule, and the dorsal paraflocculus. About 70-80% and 20-30% of the total number of labeled terminals were in the anterior and the posterior lobe, respectively; the projections were predominantly ipsilateral to the cells of origin (about 87% or more labeled terminals of the total number in each of sublobules IIb-Va). The labeled terminals were abundant in sublobule IIb (6-11%), lobule III (12-27%), and sublobules IVa (14-17%) and IVb (14-21%). In the mediolateral extent of the lobules in the anterior lobe, the labeled terminals were most numerous between 1.1 and 3.0 mm lateral to the midline (45-75% of the total number of labeled terminals on the ipsilateral side). In the posterior lobe labeled terminals were numerous in sublobule VIIIb (13.6%) and sublobule C of the paramedian lobule (15-19%). The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross sections through each lobule. In the anterior lobe the labeled terminals were distributed in eight major areas. In sublobules IIb-III, areas 1-3 were located within 1.0 mm of the midline in zone A of Voogd; areas 4-6, between 1.0 and 2.5 mm lateral to the midline in zones B-C1; and areas 7 and 8, lateral to 3.0 mm from the midline in zones C2 and C3. Areas 1-6 extended apicobasally in the middle part of the lobules. In sublobule VIIIb projections were confined to three longitudinal areas whereas in the paramedian lobule the projection areas were less distinct. The projection pattern of the lumbar DSCT was different from that of the thoracic DSCT reported previously. In the anterior lobe the thoracic DSCT projects to five areas in the medial (zone A) and the lateral part (zone B) of the vermis and to four areas in the intermediate region of the hemisphere (zones C1-C3).

Topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat.

The topographic organization of the corticonuclear fibers from the tuber vermis and paramedian lobule in the albino rat was investigated by autoradiographic anterograde tracing method. The medial portion of the tuber vermis projects to the dorsal part of the caudomedial subdivision of the medial cerebellar nucleus (MNcm), whereas the lateral portion of the tuber vermis projects to the dorsal part of the MNcm and the caudal part of the middle subdivision of the medial nucleus. The intermediate cortex of the paramedian lobule can be subdivided mediolaterally into three portions which project to the dorsolateral protuberance of the medial cerebellar nucleus, the rostrodorsal part of the posterior interpositus nucleus, and the caudodorsal part of the lateral anterior interpositus nucleus, respectively. The lateral cortex of the paramedian lobule can also be subdivided mediolaterally into two portions: the medial portion projects to the dorsolateral hump, and the lateral one to the lateral cerebellar nucleus. These results indicate that the cortical efferent fibers from the tuber vermis and paramedian lobule are clearly organized in the mediolateral direction in the albino rat.